When producing regenerated cellulose fibers by the viscose method, a reduction of chemical substances used in the process, such as carbon disulphide, will probably be necessary in the future for both environmental and economical reasons. In a traditional viscose process, the amount of carbon disulphide added in the process is between 30 and 36% by weight of the .alpha.-cellulose. To recover the outlet of carbon disulphide into the air or water is both difficult and costly.
One of the more promising ways to reduce the consumption of carbon disulphide in the viscose process and to maintain or improve good economy are to use highly reactive cellulose obtained by irradiation with ionizing particles of high energy. It is well known that the higher the reactivity of the cellulose, the lower the amount of carbon disulphide required. For example, the patent publication DE-A-2 941 624 describes a method of producing viscose from the pulp irradiated with electron beams. In the patent, it is stated that a viscose solution is produced by using a content of 24-28% by weight of carbon disulphide based on the .alpha.-cellulose at the xanthation instead of the conventional 30-36% by weight. The .alpha.-cellulose content and the sodium hydroxide content were 8% and 5.8% respectively based on the weight of the viscose solution.
The Russian patent 1 669 916 also describes a method of producing viscose from irradiated .alpha.-cellulose. In the process, the xanthation is performed by using 10-15% by weight of carbon disulphide. The viscose produced contained 8.4% by weight of .alpha.-cellulose and 6.4% by weight of sodium hydroxide.
The properties of the viscose solutions prepared from irradiated cellulose with low amounts of carbon disulphide differ significantly from the properties of conventional viscose solutions. Thus, the viscose solution of the Russian patent has
a low degree of etherification (cs.sub.2 is from 22 to 25 instead of from 45-50), PA1 a low amount of by-products (1.5-2.5% by weight instead of from 10-14% by weight), PA1 a low maturity index (9-12 ml measured by 1 N NH.sub.4 Cl instead of 18-21 ml), PA1 a high viscosity (120-135 sec measured by a falling ball instead of 50-60 sec).
However, regenerated cellulose fibers produced from viscose solutions obtained from irradiated .alpha.-cellulose exhibit unsatisfactory tensile strength. Thus, the journal "Chemical Fibers International" 1996 reports that it is possible to produce viscose fibers with tensile strength of 190-200 m N/tex and 18-20% elongation from irradiated .alpha.-cellulose with low amounts of carbon disulphide. Better results are not possible to achieve due to the properties of the viscose solution itself.
The objectives of the present invention are to provide an improved process for the production of a viscose solution in relationship to the traditional viscose method from an environmental point of view and to produce a viscose solution with suitable properties for the production of regenerated fibers. For example the spinnability of the viscose solution and the strength of the fibers are to be improved.